Piezoelectric inkjet print heads often include an actuator assembly, which can include an array of piezoelectric transducers attached to a flexible diaphragm. When a current is supplied to a piezoelectric transducer, typically through electrical connection with an electrode, the piezoelectric transducer bends or deflects. The deflection of the piezoelectric transducer causes the diaphragm to flex. Flexing the diaphragm displaces a volume of ink from a chamber, generally pushing it through a nozzle. When the current is removed from the piezoelectric transducer, the diaphragm returns to its original position, drawing ink into the chamber from a main ink reservoir through an opening, thus replacing the expelled ink.
To provide such an actuator assembly, an adhesive layer is initially applied to the array of transducers. The adhesive layer is applied with apertures extending therethrough, with the apertures being aligned with the piezoelectric transducers. Conductive epoxy (e.g., silver epoxy) is then stenciled or otherwise inserted into the aperture. An electrically conductive metallization, often referred to as a flexible printed circuit, is then positioned over the adhesive and epoxy layer. The flexible printed circuit generally includes conductive traces leading to electrical contacts (or “contact pads”). The contact pads are electrically coupled with the piezoelectric transducers via the conductive epoxy. Accordingly, electrical current can be selectively applied to a specified piezoelectric transducer along a path proceeding through a trace, to a contact, through the conductive epoxy, and to the piezoelectric transducer.
Although this approach is satisfactory for a variety of print heads, the conductive epoxy is known to extrude out of the apertures, as the diaphragm flexes and moves during operation. This can result in the conductive epoxy forming an unintended electrical path from traces and/or contacts adjacent the aligned contact to the transducer and/or to adjacent transducers. Accordingly, this extruding of the epoxy can ground or short the power circuit and/or result in unintended actuation of adjacent transducers.
To overcome this challenge, embossed or “bumped” flexible printed circuits have been successfully implemented. In bumped flexible printed circuits, the flexible printed circuit itself is deformed at the contact pad, such that the flexible printed circuit extends outward from the remainder, nominally planar, portion of the flexible printed circuit, forming the characteristic bump. When the flexible printed circuit is received onto the adhesive layer, the contacts extend through the apertures in the adhesive layer and physically contact the piezoelectric transducer, obviating a need for conductive epoxy.
However, a challenge experienced with such bumped designs results from the mechanical coupling of the flexing piezoelectric transducer with the flexible printed circuit. That is, with physical contact between the flexible printed circuit and the piezoelectric transducer, the flexible printed circuit tends to move along with the piezoelectric transducer. In contrast, such movement is generally isolated from the flexible printed circuit in non-bumped, conductive-epoxy embodiments, as the conductive epoxy generally has a low modulus and tends to avoid transmitting such motion. In the bumped flexible printed circuits, this movement can also be mitigated by maintaining a low modulus in the flexible printed circuit itself; however, there is a lower limit on the modulus of the flexible printed circuit, so as to preserve structural integrity.
In many situations, the actuators are spaced apart far enough, such that the movement in the flexible printed circuit caused by the mechanical coupling is of little or no consequence. However, as actuator density increases, enabling increased-resolution printing, the actuators are placed closer and closer together in the print head. Accordingly, in some situations, the movement of the flexible printed circuit can affect adjacent actuators, for example, causing the diaphragms to move slightly even though no current has been supplied to the transducer in the adjacent actuator. This occurrence, often referred to as “cross-talk,” can result in an artificial upper limit on the density of the actuators on the print head.
What is needed, then, are improved apparatus and methods for limiting physical coupling between adjacent actuators.